Description

The mount utility attaches a named resource to the file system hierarchy
at the pathname location mount_point, which must already exist. If mount_point has
any contents prior to the mount operation, the contents remain hidden until
the resource is once again unmounted.

If the resource is listed in the /etc/vfstab file, the command line
can specify either resource or mount_point, and mount consults /etc/vfstab for more
information. If the -F option is omitted, mount takes the file system type
from /etc/vfstab.

If the resource is not listed in the /etc/vfstab file, then the
command line must specify both the resource and the mount_point.

host can be an IPv4 or IPv6 address string. As IPv6 addresses
already contain colons, enclose host in a pair of square brackets when
specifying an IPv6 address string. Otherwise the first occurrence of a colon
can be interpreted as the separator between the host name and path, for
example, [1080::8:800:200C:417A]:tmp/file. See inet(7P) and inet6(7P).

host:pathname

Where host is the name of the NFS server host, and pathname is the path name of the directory on the server being mounted. The path name is interpreted according to the server's path name parsing rules and is not necessarily slash-separated, though on most servers, this is the case.

nfs://host[:port]/pathname

This is an NFS URL and follows the standard convention for NFS URLs as described in NFS URL Scheme, RFC 2224. See the discussion of URL's and the public option under NFS FILE SYSTEMS for a more detailed discussion.

host:pathnamenfs://host[:port]/pathname

host:pathname is a comma-separated list of host:pathname.

See the discussion of replicated file systems and failover under NFS FILE SYSTEMS for a more detailed discussion.

hostlistpathname

hostlist is a comma-separated list of hosts.

See the discussion of replicated file systems and failover under NFS FILE SYSTEMS for a more detailed discussion.

The mount command maintains a table of mounted file systems in /etc/mnttab,
described in mnttab(4).

mount_nfs supports both NFSv3 and NFSv4 mounts. The default NFS version is
NFSv4.

Options

See mount(1M) for the list of supported generic_options. See share_nfs(1M) for a
description of server options.

-ospecific_options

Set file system specific options according to a comma-separated list with no intervening spaces.

acdirmax=n

Hold cached attributes for no more than n seconds after directory update. The default value is 60.

acdirmin=n

Hold cached attributes for at least n seconds after directory update. The default value is 30.

acregmax=n

Hold cached attributes for no more than n seconds after file modification. The default value is 60.

acregmin=n

Hold cached attributes for at least n seconds after file modification. The default value is 3.

actimeo=n

Set min and max times for regular files and directories to n seconds. See “File Attributes,” below, for a description of the effect of setting this option to 0.

See “Specifying Values for Attribute Cache Duration Options,” below, for a description of how acdirmax, acdirmin, acregmax, acregmin, and actimeo are parsed on a mount command line.

bg | fg

If the first attempt fails, retry in the background, or, in the foreground. The default is fg.

forcedirectio | noforcedirectio

If forcedirectio is specified, then for the duration of the mount, forced direct I/O is used. If the filesystem is mounted using forcedirectio, data is transferred directly between client and server, with no buffering on the client. If the filesystem is mounted using noforcedirectio, data is buffered on the client. forcedirectio is a performance option that is of benefit only in large sequential data transfers. The default behavior is noforcedirectio.

grpid

By default, the GID associated with a newly created file obeys the System V semantics; that is, the GID is set to the effective GID of the calling process. This behavior can be overridden on a per-directory basis by setting the set-GID bit of the parent directory; in this case, the GID of a newly created file is set to the GID of the parent directory (see open(2) and mkdir(2)). Files created on file systems that are mounted with the grpid option obeys BSD semantics independent of whether the set-GID bit of the parent directory is set; that is, the GID is unconditionally inherited from that of the parent directory.

hard | soft

Continue to retry requests until the server responds (hard) or give up and return an error (soft). The default value is hard. Note that NFSv4 clients do not support soft mounts.

intr | nointr

Allow (do not allow) keyboard interrupts to kill a process that is hung while waiting for a response on a hard-mounted file system. The default is intr, which makes it possible for clients to interrupt applications that can be waiting for a remote mount.

noac

Suppress data and attribute caching. The data caching that is suppressed is the write-behind. The local page cache is still maintained, but data copied into it is immediately written to the server.

nocto

Do not perform the normal close-to-open consistency. When a file is closed, all modified data associated with the file is flushed to the server and not held on the client. When a file is opened the client sends a request to the server to validate the client's local caches. This behavior ensures a file's consistency across multiple NFS clients. When -nocto is in effect, the client does not perform the flush on close and the request for validation, allowing the possiblity of differences among copies of the same file as stored on multiple clients.

This option can be used where it can be guaranteed that accesses to a specified file system are made from only one client and only that client. Under such a condition, the effect of -nocto can be a slight performance gain.

port=n

The server IP port number. The default is NFS_PORT. If the port option is specified, and if the resource includes one or more NFS URLs, and if any of the URLs include a port number, then the port number in the option and in the URL must be the same.

posix

Request POSIX.1 semantics for the file system. Requires a mount Version 2 mountd(1M) on the server. See standards(5) for information regarding POSIX.

proto=netid | rdma

By default, the transport protocol that the NFS mount uses is the first available TCP transport supported both by the client and the server. If no TCP transport is found, then it attempts to use a UDP transport, as ordered in the /etc/netconfig file.

Use this option to override the default behavior.

proto is set to the value of netid or rdma. netid is the value of the network_id field entry in the /etc/netconfig file.

The UDP protocol is not supported for NFS Version 4. If you specify a UDP protocol with the proto option, NFS version 4 is not used.

public

The public option forces the use of the public file handle when connecting to the NFS server. The resource specified might not have an NFS URL. See the discussion of URLs and the public option under NFS FILE SYSTEMS for a more detailed discussion.

quota | noquota

Enable or prevent quota(1M) to check whether the user is over quota on this file system; if the file system has quotas enabled on the server, quotas are still checked for operations on this file system.

remount

Remounts a read-only file system as read-write (using the rw option). This option cannot be used with other -o options, and this option works only on currently mounted read-only file systems.

retrans=n

Set the number of NFS retransmissions to n. The default value is 5. For connection-oriented transports, this option has no effect because it is assumed that the transport performs retransmissions on behalf of NFS.

retry=n

The number of times to retry the mount operation. The default for the mount command is 10000.

The default for the automounter is 0, in other words, do not retry. You might find it useful to increase this value on heavily loaded servers, where automounter traffic is dropped, causing unnecessary server not responding errors.

rsize=n

Set the read buffer size to a maximum of n bytes. The default value is 1048576 when using connection-orientated transports with Version 3 or Version 4 of the NFS protocol, and 32768 when using connection-less transports. The default can be negotiated down if the server prefers a smaller transfer size. “Read” operations may not necessarily use the maximum buffer size. When using Version 2, the default value is 32768 for all transports.

sec=mode

Set the security mode for NFS transactions. If sec= is not specified, then the default action is to use AUTH_SYS over NFS Version 2 mounts, or to negotiate a mode over NFS Version 3 or Version 4 mounts.

NFS Version 3 mounts negotiate a security mode when the server returns an array of security modes. The client picks the first mode in the array that is supported on the client. In negotiations, an NFS Version 3 client is limited to the security flavors listed in /etc/nfssec.conf.

NFS Version 4 mounts negotiate a security mode when the server returns an array of security modes. The client attempts the mount with each security mode, in order, until one is successful.

Only one mode can be specified with the sec= option. See nfssec(5) for the available mode options.

secure

This option has been deprecated in favor of the sec=dh option.

timeo=n

Set the NFS timeout to n tenths of a second. The default value is 11 tenths of a second for connectionless transports, and 600 tenths of a second for connection-oriented transports. This value is ignored for connectionless transports. Such transports might implement their own timeouts, which are outside the control of NFS.

vers=NFS version number

By default, the version of NFS protocol used between the client and the server is the highest one available on both systems. The default maximum for the client is Version 4. This can be changed by setting the NFS_CLIENT_VERSMAX parameter in /etc/default/nfs to a valid version (2, 3, or 4). If the NFS server does not support the client's default maximum, the next lowest version attempted until a matching version is found.

wsize=n

Set the write buffer size to a maximum of n bytes. The default value is 1048576 when using connection-orientated transports with Version 3 or Version 4 of the NFS protocol, and 32768 when using connection-less transports. The default can be negotiated down if the server prefers a smaller transfer size. “Write” operations may not necessarily use the maximum buffer size. When using Version 2, the default value is 32768 for all transports.

xattr | noxattr

Allow or disallow the creation and manipulation of extended attributes. The default is xattr. See fsattr(5) for a description of extended attributes.

-O

Overlay mount. Allow the file system to be mounted over an existing mount point, making the underlying file system inaccessible. If a mount is attempted on a pre-existing mount point without setting this flag, the mount fails, producing the error “device busy.”

NFS FILE SYSTEMS

Background versus Foreground

File systems mounted with the bg option indicate that mount is to retry in the background if the server's mount daemon (mountd(1M)) does not respond. mount retries the request up to the count specified in the retry=n option. (Note that the default value for retry differs between mount and automount. See the description of retry, above.) Once the file system is mounted, each NFS request made in the kernel waits timeo=n tenths of a second for a response. If no response arrives, the time-out is multiplied by 2 and the request is retransmitted. When the number of retransmissions has reached the number specified in the retrans=n option, a file system mounted with the soft option returns an error on the request; one mounted with the hard option prints a warning message and continues to retry the request.

Hard versus Soft

File systems that are mounted read-write or that contain executable files should always be mounted with the hard option. Applications using soft mounted file systems can incur unexpected I/O errors, file corruption, and unexpected program core dumps. The soft option is not recommended.

Authenticated requests

The server can require authenticated NFS requests from the client. sec=dh authentication might be required. See nfssec(5).

URLs and the public option

If the public option is specified, or if the resource includes and NFS URL, mount attempts to connect to the server using the public file handle lookup protocol. See WebNFS Client Specification, RFC 2054. If the server supports the public file handle, the attempt is successful; mount does not need to contact the server's rpcbind(1M) and the mountd(1M) daemons to get the port number of the mount server and the initial file handle of pathname, respectively. If the NFS client and server are separated by a firewall that allows all outbound connections through specific ports, such as NFS_PORT, then this enables NFS operations through the firewall. The public option and the NFS URL can be specified independently or together. They interact as specified in the following matrix:

Resource Style
host:pathname NFS URL
public option Force public file Force public file
handle and fail handle and fail
mount if not supported. mount if not supported.
Use Native paths. Use Canonical paths.
default Use MOUNT protocol. Try public file handle
with Canonical paths.
Fall back to MOUNT
protocol if not
supported.

A Native path is a path name that is interpreted according to conventions used on the native operating system of the NFS server. A Canonical path is a path name that is interpreted according to the URL rules. See Uniform Resource Locators (URL), RFC 1738. See Examples for uses of Native and Canonical paths.

Replicated file systems and failover

resource can list multiple read-only file systems to be used to provide data. These file systems should contain equivalent directory structures and identical files. It is also recommended that they be created by a utility such as rdist(1). The file systems can be specified either with a comma-separated list of host:/pathname entries and/or NFS URL entries, or with a comma -separated list of hosts, if all file system names are the same. If multiple file systems are named and the first server in the list is down, failover uses the next alternate server to access files. If the read-only option is not chosen, replication is disabled. File access, for NFS Versions 2 and 3, is blocked on the original if NFS locks are active for that file.

File Attributes

To improve NFS read performance, files and file attributes are cached. File
modification times get updated whenever a write occurs. However, file access times
can be temporarily out-of-date until the cache gets refreshed.

The attribute cache retains file attributes on the client. Attributes for a
file are assigned a time to be flushed. If the file is
modified before the flush time, then the flush time is extended by
the time since the last modification (under the assumption that files that
changed recently are likely to change soon). There is a minimum and maximum
flush time extension for regular files and for directories. Setting actimeo=n sets
flush time to n seconds for both regular files and directories.

Setting actimeo=0 disables attribute caching on the client. This means that every
reference to attributes is satisfied directly from the server though file data
is still cached. While this guarantees that the client always has the
latest file attributes from the server, it has an adverse effect on performance
through additional latency, network load, and server load.

Setting the noac option also disables attribute caching, but has the further
effect of disabling client write caching. While this guarantees that data written
by an application is written directly to a server, where it can
be viewed immediately by other clients, it has a significant adverse effect on
client write performance. Data written into memory-mapped file pages (mmap(2)) are not
written directly to this server.

Specifying Values for Attribute Cache Duration Options

The attribute cache duration options are acdirmax, acdirmin, acregmax, acregmin, and actimeo,
as described under OPTIONS. A value specified for actimeo sets the values
of all attribute cache duration options except for any of these options specified
following actimeo on a mount command line. For example, consider the following
command:

example# mount -o acdirmax=10,actimeo=1000 server:/path /localpath

Because actimeo is the last duration option in the command line, its
value (1000) becomes the setting for all of the duration options, including
acdirmax. Now consider:

example# mount -o actimeo=1000,acdirmax=10 server:/path /localpath

Because the acdirmax option follows actimeo on the command line, it is
assigned the value specified (10). The remaining duration options are set to
the value of actimeo (1000).

Examples

Example 1 Mounting an NFS File System

To mount an NFS file system:

example# mount serv:/usr/src /usr/src

Example 2 Mounting An NFS File System Read-Only With No suid Privileges

To mount an NFS file system read-only with no suid privileges:

example# mount -r -o nosuid serv:/usr/src /usr/src

Example 3 Mounting An NFS File System Over Version 2, with the UDP Transport

To mount an NFS file system over Version 2, with the UDP
transport:

example# mount -o vers=2,proto=udp serv:/usr/src /usr/src

Example 4 Mounting an NFS File System Using An NFS URL

To mount an NFS file system using an NFS URL (a canonical
path):

example# mount nfs://serv/usr/man /usr/man

Example 5 Mounting An NFS File System Forcing Use Of The Public File Handle

To mount an NFS file system and force the use of the
public file handle and an NFS URL (a canonical path) that has
a non 7–bit ASCII escape sequence:

example# mount -o public nfs://serv/usr/%A0abc /mnt/test

Example 6 Mounting an NFS File System Using a Native Path

To mount an NFS file system using a native path (where the
server uses colons (“:”) as the component separator) and the public file
handle:

example# mount -o public serv:C:doc:new /usr/doc

Example 7 Mounting a Replicated Set of NFS File Systems with the Same Pathnames

To mount a replicated set of NFS file systems with the same
pathnames:

example# mount serv-a,serv-b,serv-c:/usr/man /usr/man

Example 8 Mounting a Replicated Set of NFS File Systems with Different Pathnames

To mount a replicated set of NFS file systems with different pathnames:

Notes

An NFS server should not attempt to mount its own file systems.
See lofs(7FS).

If the directory on which a file system is to be mounted
is a symbolic link, the file system is mounted on the directory to which the symbolic link refers, rather
than being mounted on top of the symbolic link itself.

Since the root (/) file system is mounted read-only by the kernel
during the boot process, only the remount option (and options that can
be used in conjunction with remount) affect the root (/) entry in the
/etc/vfstab file.

mount_cachefs cannot be used with replicated NFS mounts or any NFS Version
4 mount.